Sounding Reference Signal Cell Specific Sub-Frame Configuration

ABSTRACT

A method of wireless communication including a plurality of fixed basestations and a plurality of mobile user equipment with each basestation transmitting to any user equipment within a corresponding cell a sounding reference signal sub-frame configuration indicating sub-frames when sounding is permitted. Each user equipment recognizes the sounding reference signal sub-frame configuration and sounds only at permitted sub-frames. Differing cells may have differing sounding reference signal sub-frame configurations. There are numerous manners to encode the transmitted information.

CLAIM OF PRIORITY

This application claims priority under 35 U.S.C. 119(e)(1) to U.S.Provisional Application No. 61/039,571 filed Mar. 26, 2008, U.S.Provisional Application No. 61/040,752 filed Mar. 31, 2008, U.S.Provisional Application No. 61/041,694 filed Apr. 2, 2008, U.S.Provisional Application No. 61/044,636, and U.S. Provisional ApplicationNo. 61/045,421 filed Apr. 16, 2008.

TECHNICAL FIELD OF THE INVENTION

The technical field of this invention is wireless communication.

BACKGROUND OF THE INVENTION

FIG. 1 shows an exemplary wireless telecommunications network 100. Theillustrative telecommunications network includes base stations 101, 102and 103, though in operation, a telecommunications network necessarilyincludes many more base stations. Each of base stations 101, 102 and 103are operable over corresponding coverage areas 104, 105 and 106. Eachbase station's coverage area is further divided into cells. In theillustrated network, each base station's coverage area is divided intothree cells. Handset or other user equipment (UE) 109 is shown in Cell A108. Cell A 108 is within coverage area 104 of base station 101. Basestation 101 transmits to and receives transmissions from UE 109. As UE109 moves out of Cell A 108 and into Cell B 107, UE 109 may be handedover to base station 102. Because UE 109 is synchronized with basestation 101, UE 109 can employ non-synchronized random access toinitiate handover to base station 102.

Non-synchronized UE 109 also employs non-synchronous random access torequest allocation of up-link 111 time or frequency or code resources.If UE 109 has data ready for transmission, which may be traffic data,measurements report, tracking area update, UE 109 can transmit a randomaccess signal on up-link 111. The random access signal notifies basestation 101 that UE 109 requires up-link resources to transmit the UE'sdata. Base station 101 responds by transmitting to UE 109 via down-link110, a message containing the parameters of the resources allocated forUE 109 up-link transmission along with a possible timing errorcorrection. After receiving the resource allocation and a possibletiming advance message transmitted on down-link 110 by base station 101,UE 109 optionally adjusts its transmit timing and transmits the data onup-link 111 employing the allotted resources during the prescribed timeinterval.

FIG. 2 shows the Evolved Universal Terrestrial Radio Access (E-UTRA)time division duplex (TDD) Frame Structure. Different sub-frames areallocated for downlink (DL) or uplink (UL) transmissions. Table 1 showsapplicable DL/UL sub-frame allocations.

TABLE 1 Con- Switch-point Sub-frame number figuration periodicity 0 1 23 4 5 6 7 8 9 0  5 ms D S U U U D S U U U 1  5 ms D S U U D D S U U D 2 5 ms D S U D D D S U D D 3 10 ms D S U U U D D D D D 4 10 ms D S U U DD D D D D 5 10 ms D S U D D D D D D D 6 10 ms D S U U U D S U U D

SUMMARY OF THE INVENTION

This invention addresses the timing aspects of sounding reference signal(SRS) transmission, also with the goal of reducing SIB (broadcast) andthe radio resource control (RRC) overhead. Overall, the parametersrelated to SRS timing are: SRS sub-frame configuration (SIB signaled);SRS duration (RRC signaled); SRS periodicity (RRC signaled) andsub-frame offset (RRC signaled).

BRIEF DESCRIPTION OF THE DRAWINGS

These and other aspects of this invention are illustrated in thedrawings, in which:

FIG. 1 is a diagram of a communication system of the prior art relatedto this invention having three cells;

FIG. 2 shows the Evolved Universal Terrestrial Radio Access (E-UTRA) TDDFrame Structure of the prior art;

FIG. 3 illustrates a first example binary tree used in encoding;

FIG. 4 illustrates a second example binary tree used in encoding;

FIG. 5 illustrates a first resource sharing tree for a first set ofperiodicities and offsets; and

FIG. 6 illustrates a second resource sharing tree for a second set ofperiodicities and offsets.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Sounding involves exchange of signals between the base station and theconnected UE. Each sounding uses a reference resource identifierselected from an available reference resource identifier map h(t, L) anda portion of the spectrum selected from an available spectrum identifiermap f(t, N); where L is a group of shared parameters signaled to each UEfrom the group; and N is a group of shared parameters signaled to eachUE from the group. Some examples utilize CAZAC sequences as thereference sequences. CAZAC sequences are complex-valued sequences with:constant amplitude (CA); and zero cyclic autocorrelation (ZAC). Examplesof CAZAC sequences include: Chu sequences, Frank-Zadoff sequences,Zadoff-Chu (ZC) sequences and generalized chirp-like (GCL) sequences.CAZAC (ZC or otherwise) sequences are presently preferred.

In this invention each basestation 101, 102 and 103 transmits a soundingreference signal (SRS) to connected UEs 109 in the corresponding cell.The UE receiving the SRS then conducts sounding in accordance with theSRS sub-frame configuration.

The SRS sub-frame configuration is broadcast by basestation 101 in SIB.This sub-frame configuration indicates which sub-frames are SRSsub-frames. Broadcast of the SRS sub-frame configuration is useful evenfor UEs 109 which do not transmit any SRS. SRS shouldn't collide withphysical uplink shared channel (PUSCH) transmission. Thus non-SRS UEs109 can extract some of their silent symbol periods from the SRSsub-frame configuration. These silent periods are useful for performingsome measurements at UE 109. In general each cell 107 and 108 wouldemploy a different SRS sub-frame configuration. Ideally, basestations101, 102 and 103 would select SRS sub-frame configurations to minimizecross-cell interference.

There are two main ways of signaling and interpreting the SRS sub-frameconfiguration parameters. Sub-frame configuration can be defined by twoparameters: the periodicity T_(SFC); and the offset Δ_(SFC). Both UEs109 and basestation 101 keep a sub-frame counter C_(SFC) permitting UE109 and basestation 101 to determine which sub-frames are configured forSRS transmission. A sub-frame is an SRS sub-frame if and only ifΔ_(SFC)=(C_(SFC))mod T_(SFC). The exact range of values of Δ_(SFC) andT_(SFC) need to be defined with the number of bits and encoding foreach. For example, T_(SFC) could be selected from the set {1, 2, 3, 4,5, . . . , 32} allowing flexible system deployment Δ_(SFC) could beselected from the same set. This yields maximum flexibility, butrequires 10 bits of broadcast SIB signaling, which can be very costly. Areduced overhead alternative encodes and signals T_(SFC) first. Thisrequires greatest integer in log₂(T_(SFC)) (ceil[log₂(T_(SFC))]) bits.The bits required for Δ_(SFC) would be either the ceil[log₂(T_(SFC))] orthe least integer in log₂(T_(SFC)) (floor[log₂(T_(SFC))]) because0≦Δ_(SFC)<T_(SFC). This reduces the number of required bits forsignaling Δ_(SFC), but only for certain scenarios where T_(SFC) issmall. Another reduced overhead alternative hard codes a value forΔ_(SFC) such as zero. In that case, only T_(SFC) is signaled.

Several examples of combined T_(SFC), Δ_(SFC) coding are listed in thefollowing tables. In these examples the SRS sub-frame configuration isencoded using either 4 or 5 bits in SIB using joint source coding inT_(SFC) and Δ_(SFC). Thus a unique 4 or 5 bit combination maps into aparticular pair (T_(SFC), Δ_(SFC)).

Table 2 lists a 4 bit example suitable for use in frequency divisionduplex (FDD) systems.

TABLE 2 Decimal Binary T_(SFC) Δ_(SFC) 0 0000 1 0 1 0001 2 0 2 0010 2 13 0011 5 0 4 0100 5 1 5 0101 5 2 6 0110 10 0 7 0111 10 1 8 1000 10 2 91001 20 0 10 1010 20 1 11 1011 20 2 12 1100 40 0 13 1101 40 1 14 1110 402 15 1111 Inf. NAIn Table 2 a coding of decimal 15 indicates no SRS thus T_(SFC) isinfinite, Δ_(SFC) is meaningless and not applicable (NA).

Table 3 lists another 4 bit example suitable for use in FDD systems.

TABLE 3 Decimal Binary T_(SFC) Δ_(SFC) 0 0000 1 0 1 0001 2 0 2 0010 2 13 0011 5 2 4 0100 5 3 5 0101 5 4 6 0110 10 5 7 0111 10 6 8 1000 10 7 91001 20 8 10 1010 20 9 11 1011 20 10 12 1100 40 11 13 1101 40 12 14 111040 13 15 1111 Inf. NAIn Table 3 a coding of decimal 15 indicates no SRS thus T_(SFC) isinfinite, Δ_(SFC) is meaningless and not applicable (NA).

Table 4 lists a 5 bit example suitable for use in FDD systems.

TABLE 4 Decimal Binary T_(SFC) Δ_(SFC) 0 00000 1 0 1 00001 2 0 2 00010 21 3 00011 5 0 4 00100 5 1 5 00101 5 2 6 00110 5 3 7 00111 5 4 8 01000 100 9 01001 10 1 10 01010 10 2 11 01011 10 3 12 01100 10 4 13 01101 10 514 01110 10 6 15 01111 20 0 16 10000 20 1 17 10001 20 2 18 10010 20 3 1910011 20 4 20 10100 20 5 21 10101 20 6 22 10110 40 0 23 10111 40 1 2411000 40 2 25 11001 40 3 26 11010 40 4 27 11011 40 5 28 11100 40 6 2911101 Optional 30 11110 Optional 31 11111 Inf. NAIn Table 4 codings decimal 29 and 30 are optional and not defined inthis example. In Table 4 a coding of decimal 31 indicates no SRS thusT_(SFC) is infinite, Δ_(SFC) is meaningless and not applicable (NA).

Table 5 lists another 5 bit example suitable for use in FDD systems.

TABLE 5 Decimal Binary T_(SFC) Δ_(SFC) 0 00000 1 0 1 00001 2 0 2 00010 21 3 00011 5 0 4 00100 5 1 5 00101 5 2 6 00110 5 3 7 00111 5 4 8 01000 100 9 01001 10 1 10 01010 10 2 11 01011 10 3 12 01100 10 4 13 01101 10 514 01110 10 6 15 01111 10 7 16 10000 20 0 17 10001 20 1 18 10010 20 2 1910011 20 3 20 10100 20 4 21 10101 20 5 22 10110 20 6 23 10111 20 7 2411000 40 0 25 11001 40 1 26 11010 40 2 27 11011 40 3 28 11100 40 4 2911101 40 5 30 11110 40 6 31 11111 Inf. NAIn Table 5 a coding of decimal 31 indicates no SRS thus T_(SFC) isinfinite, Δ_(SFC) is meaningless and not applicable (NA).

Table 6 lists another 5 bit example suitable for use in FDD systems.

TABLE 6 Decimal Binary T_(SFC) Δ_(SFC) 0 00000 1 0 1 00001 2 0 2 00010 21 3 00011 5 0 4 00100 5 1 5 00101 5 2 6 00110 5 3 7 00111 5 4 8 01000 103 9 01001 10 4 10 01010 10 5 11 01011 10 6 12 01100 10 7 13 01101 10 814 01110 10 9 15 01111 20 10 16 10000 20 11 17 10001 20 12 18 10010 2013 19 10011 20 14 20 10100 20 15 21 10101 20 16 22 10110 40 17 23 1011140 18 24 11000 40 19 25 11001 40 20 26 11010 40 21 27 11011 40 22 2811100 40 23 29 11101 Optional 30 11110 Optional 31 11111 Inf. NAIn Table 6 codings decimal 29 and 30 are optional and not defined inthis example. In Table 6 a coding of decimal 31 indicates no SRS thusT_(SFC) is infinite, Δ_(SFC) is meaningless and not applicable (NA).

Table 7 lists a 4 bit example suitable for use in time division duplex(TDD) systems.

TABLE 7 Decimal Binary T_(SFC) Δ_(SFC) 0 0000 1 0 1 0001 5 1 (a) 2 00105 1 (b) 3 0011 5 2 4 0100 10 0 5 0101 10 1 (a) 6 0110 10 1 (b) 7 0111 102 8 1000 20 0 9 1001 20 1 (a) 10 1010 20 1 (b) 11 1011 20 2 12 1100 40 013 1101 40 1 (a) 14 1110 40 1 (b) 15 1111 Inf. NAIn Table 7 codings decimal 1, 2, 5, 6, 9, 10, 13 and 14 are encoded withrespect to UpPTS orthogonal frequency division multiplexing (OFDM)symbols. If UpPTS contains two OFDM symbols: 1(a) means the first OFDMsymbol is used for SRS to determine Δ_(SFC); and 1(b) means the secondof OFDM symbol is used for SRS to determine Δ_(SFC). In Table 7 a codingof decimal 15 indicates no SRS thus T_(SFC) is infinite, Δ_(SFC) ismeaningless and not applicable (NA).

Table 8 lists a 5 bit example suitable for use in TDD systems.

TABLE 8 Decimal Binary T_(SFC) Δ_(SFC) 0 00000 1 0 1 00001 5 1 (a) 200010 5 1 (b) 3 00011 5 1 (a) + 1 (b) 4 00100 5 2 5 00101 5 3 6 00110 54 7 00111 10 1 (a) 8 01000 10 1 (b) 9 01001 10 1 (a) + 1 (b) 10 01010 102 11 01011 10 3 12 01100 10 4 13 01101 10 7 14 01110 10 8 15 01111 20 1(a) 16 10000 20 1 (b) 17 10001 20 1 (a) + 1 (b) 18 10010 20 2 19 1001120 3 20 10100 20 4 21 10101 20 7 22 10110 20 8 23 10111 40 1 (a) 2411000 40 1 (b) 25 11001 40 1 (a) + 1 (b) 26 11010 40 2 27 11011 40 3 2811100 40 4 29 11101 40 7 30 11110 40 8 31 11111 Inf. NAIn Table 8 codings decimal 1, 2, 3, 7, 8, 9, 15, 16, 17, 23, 24 and 25are encoded with respect to UpPTS OFDM symbols. If UpPTS contains twoOFDM symbols: 1(a) means the first OFDM symbol is used for SRS todetermine Δ_(SFC); 1(b) means the second of OFDM symbol is used for SRSto determine Δ_(SFC); and 1(a)+1(b) means that both OFDM symbols areused for SRS to determine Δ_(SFC). In Table 8 a coding of decimal 31indicates no SRS thus T_(SFC) is infinite, Δ_(SFC) is meaningless andnot applicable (NA). For TDD, if the SRS sub-frame period is 1, all ULsub-frames and UpPTS can contain SRS. If UpPTS is used for short randomaccess channel (RACH) transmission in some sub-frames, then there is noSRS. Thus basestation 101 does not assign any SRS UEs in RACH UpPTSsub-frames.

Table 9 lists another 5 bit example suitable for use in TDD systems.

TABLE 9 Decimal Binary T_(SFC) Δ_(SFC) 0 00000 1 0 1 00001 5 1 (a) 200010 5 1 (b) 3 00011 5 1 (a) + 1 (b) 4 00100 5 2 5 00101 5 3 6 00110 54 7 00111 10 1 (a) 8 01000 10 1 (b) 9 01001 10 1 (a) + 1 (b) 10 01010 102 11 01011 10 3 12 01100 10 6 (a) 13 01101 10 6 (b) 14 01110 10 6 (a) +6 (b) 15 01111 20 1 (a) 16 10000 20 1 (b) 17 10001 20 1 (a) + 1 (b) 1810010 20 2 19 10011 20 3 20 10100 20 6 (a) 21 10101 20 6 (b) 22 10110 206 (a) + 6 (b) 23 10111 40 1 (a) 24 11000 40 1 (b) 25 11001 40 1 (a) + 1(b) 26 11010 40 2 27 11011 40 3 28 11100 40 6 (a) 29 11101 40 6 (b) 3011110 40 6 (a) + 6 (b) 31 11111 Inf. NAIn Table 9 codings decimal 1, 2, 3, 7, 8, 9, 12 to 17, 20 to 25, 28, 29and 30 are encoded with respect to UpPTS OFDM symbols. If UpPTS containstwo OFDM symbols: 1(a) means the first OFDM symbol is used for SRS todetermine Δ_(SFC); 1(b) means the second of OFDM symbol is used for SRSto determine Δ_(SFC); and 1(a)+1(b) means that both OFDM symbols areused for SRS to determine Δ_(SFC). In Table 8 a coding of decimal 31indicates no SRS thus T_(SFC) is infinite, Δ_(SFC) is meaningless andnot applicable (NA).

Table 10 lists another 4 bit example suitable for use in FDD systems.Sounding reference signal sub-frames are the sub-frames satisfying└n_(s)/2┘mod T_(SFC)εΔ_(SFC).

TABLE 10 Decimal Binary T_(SFC) Δ_(SFC) 0 0000 1 0 1 0001 2 0 2 0010 2 13 0011 5 0 4 0100 5 1 5 0101 5 2 6 0110 5 3 7 0111 5 0, 1 8 1000 5 2, 39 1001 10 0 10 1010 10 1 11 1011 10 2 12 1100 10 3 13 1101 10 0, 1, 2,3, 4, 6, 8 14 1110 10 0, 1, 2, 3, 4, 5, 6, 8 15 1111 reserved reserved

Table 11 lists another 4 bit example suitable for use in TDD systems.Sounding reference signal sub-frames are the sub-frames satisfying└n_(s)/2┘mod T_(SFC)εΔ_(SFC). Sounding reference signals are transmittedonly in configured UL sub-frames or UpPTS.

TABLE 11 Decimal Binary T_(SFC) Δ_(SFC) 0 0000 5 1 1 0001 5 1, 2 2 00105 1, 3 3 0011 5 1, 4 4 0100 5 1, 2, 3 5 0101 5 1, 2, 4 6 0110 5 1, 3, 47 0111 5 1, 2, 3, 4 8 1000 10 1, 2, 6 9 1001 10 1, 3, 6 10 1010 10 1, 6,7 11 1011 10 1, 2, 6, 8 12 1100 10 1, 3, 6, 9 13 1101 10 1, 4, 6, 7 141110 reserved reserved 15 1111 reserved reserved

For TDD, a SRS sub-frame period of 1 means that all UL sub-frames andUpPTS can contain SRS. If UpPTS is used for short RACH transmission insome sub-frames, then there is no SRS. Thus basestation 101 does notassign any SRS UEs in RACH UpPTS sub-frames. For TDD, it is not clearhow to have SRS sub-frame configuration with period 2.

Broadcasting both Δ_(SFC) and T_(SFC) supports flexible SRS sub-frameconfiguration. Different values of Δ_(SFC) can be assigned in differentcells. Thus SRS transmission in one cell does not interfere with aneighboring cells. Because the set of UL sub-frames varies with DL/ULsub-frame configuration, Δ_(SFC) is needed for SRS sub-frameconfiguration in TDD. Note binary tree 300 illustrates in FIG. 3 is justan example. Different trees can be used with different depths andconfigurations and different joint source-encodings of (Δ_(SFC),T_(SFC)).

FIG. 3 illustrates a manner of jointly encoding Δ_(SFC) and T_(SFC) withan efficient source code to support multiple values for the offsetΔ_(SFC) for each T_(SFC) using an underlying structure. FIG. 3illustrates a binary tree based structure 300. Binary tree 300 hasexactly 2^(x)−1 nodes, where x is 4 in this example. Identifying anypoint on the binary tree requires exactly x bits, 4 bits in thisexample. A reserved codeword may be defined meaning no SRS, for example.Each node in the binary tree is assigned a mapping to a pair of(Δ_(SFC), T_(SFC)). The simplest mapping is that nodes at a certaindepth are assigned a unique value of T_(SFC). Referring to FIG. 3, fornode 1 T_(SFC)=L, for nodes (2, 3) T_(SFC)=2, for nodes (4, 5, 6, 7)T_(SFC)=3, and for nodes (8, 9, 10, 11, 12, 13, 14 and 15) T_(SFC)=3.Thus the depth identifies T_(SFC). In this example offset Δ_(SFC) isderived from the value of the node mod T_(SFC). Such code is evensimpler if we consider binary values for labeled nodes. The position ofthe most significant 1 bit in the binary value of a node equals thevalue of T_(SFC). This is illustrated in FIG. 3. The remaining lesssignificant bits identify offset Δ_(SFC). This same binary code can beused to encode frequency position (offset and bandwidth) of SRS.

FIG. 4 illustrates another embodiment of this invention. Binary tree 400illustrated in FIG. 4 identifies sub-frames having periodicities T_(SFC)of (1, 2, 4, 8, 16) ms. Each node in binary tree 400 is mapped to a pairof (Δ_(SFC), T_(SFC)). The simplest mapping assigns a unique value ofT_(SFC) to all nodes at a certain depth. FIG. 4 illustrates thisassignment. A simple 5-bit code identifies the node. The position ofmost significant 1 identifies T_(SFC) as 2^((N-1)). The remaining bitsidentify the offset Δ_(SFC). If all 0 is signaled (00000), thisidentifies no SRS (infinity) or alternatively a one-shot SRS.

In another embodiment of the invention, the pair (Δ_(SFC), T_(SFC)) iscoded jointly (source encoding) and broadcast in the SIB. In thisembodiment the tree structure is not necessary. For example, if T_(SFC)takes on values from the set (1, 2, 4, 5, 10) ms, then there are1+2+4+5+10=22 possible values for the combination (Δ_(SFC), T_(SFC)).Each one of these combinations is mapped to a unique number Y out 22numbers and can be represented by 5 bits. Broadcasting the unique numberidentifies the (Δ_(SFC), T_(SFC)) pair. Broadcasting the unique numbercould be in binary. In this example, 5 bits are need to represent the 22possible values of Y. One option maps the range of Y into T_(SFC). Then(Y)mod T_(SFC) identifies Δ_(SFC).

Suppose T_(SFC) can have values from the set (A₁, A₂, A_(N)) ms. Thereare A₁+A₂+ . . . +A_(N) values for the communicated number Y. Thisrequires ceil[log₂(A₁+A₂+ . . . +A_(N))] bits to represent. The valuesof T_(SFC) and Δ_(SFC) are encoded as follows. If Y is in the range 1 toA₁ then T_(SFC) is A₁. If Y is in the range 1+A₁ to A₁+A₂ then T_(SFC)is A₂. If Y is in the range 1+A₁+ . . . +A_(K) to A₁+ . . .+A_(K)+A_(K+1) then T_(SFC) is A_(K+1). The value of Δ_(SFC) isdetermined as (Y)mod T_(SFC). Any remaining values of Y which do not mapinto (Δ_(SFC), T_(SFC)) can be used to communicate re-configuration,one-shot SRS or other options.

In another embodiment of the invention, the SRS sub-frame configurationmay not be exactly qui-spaced. In this embodiment introduces anotherparameter δ_(SFC). Then, the SRS sub-frames are the sub-frames C_(SFC)for which any of the following equations hold:

Δ_(SFC)=C_(SFC) mod T_(SFC)

1+Δ_(SFC) =C _(SFC) mod T_(SFC)

2+Δ_(SFC) =C _(SFC) mod T_(SFC)

δ_(SFC)+Δ_(SFC) =C _(SFC) mod T_(SFC)

The value of the parameter δ_(SFC) can be pre-determined and fixed. Inthis case the value of δ_(SFC) can be inferred from the cell ID.Alternatively, the value of δ_(SFC) can be signaled in the SIB. As afurther alternative, the value of δ_(SFC) can be encoded jointly orseparately with T_(SFC) and Δ_(SFC).

In other embodiments of the invention, multiple values for T_(SFC),Δ_(SFC) and δ_(SFC) are possible. These values can also be broadcast viaSIB.

RRC signaled SRS timing parameters include: duration having a range fromone-shot to infinite; periodicity indicating the SRS transmission periodfrom the UE 109; and sub-frame offset identifying the offset within theSRS transmission period from the UE.

In a first embodiment the RRC overhead for SRS timing parametersinclude: duration is one-shot to infinite and can be encoded in one bit;periodicity selected from (2, 5, 10, 20, 40, 80, 160, 320) ms which canbe encoded in 3 bits; and sub-frame offset which must be designedaccording to the worst case of the longest possible periodicity thusrequiring ceil[log₂(320)] or 9 bits to encode. Thus the number of UEspecific bits signaled via RRC to describe the SRS configuration in thisexample equals 1+3+9=13 bits. Since the cell wide sub-frameconfiguration is separate from the UE specific parameters listed above,there are either two possibilities.

The number of bits and source encoding required for UE specificparameters could depend on the actual sub-frame configurationtransmitted via SIB. For example, if the sub-frame configuration notesevery sub-frame is an SRS sub-frame, then 1+3+9=13 bits are required tospecify the UE specific parameters. Alternatively, if the sub-frameconfiguration notes that every tenth sub-frame is an SRS sub-frame, thena smaller number of bits would be required to specify the UE specificparameters. This approach is more cumbersome. It likely would require adifferent definition of RRC configured parameters, depending on thesub-frame configuration. This would disadvantageously further complicatethe specification. The number of bits required for UE specific RRCparameters can be independent of the actual sub-frame configurationtransmitted via SIB. The worst case sub-frame configuration is when allsub-frames are SRS sub-frames. The number of RRC configured SRS timingparameters is this worst case is 1+3+9=13 bits.

In the second option there are two SRS periods that are not multiples ofeach other and cannot be multiplexed on a common SRS (frequency)resource. Possible SRS periods are selected from the set (2, 5, 10, 20,40, 80, 160, 320) ms. Thus, since 2 ms and 5 ms cannot be multiplexed,any given SRS resource should be shared either with periodicitiesselected from the set S (5, 10, 20, 40, 80, 160, 320) ms or set S2 (2,10, 20, 40, 80, 160, 320) ms. FIG. 5 illustrates a resource sharing tree500 for set S1. Tree 500 for set S1 illustrated in FIG. 5 has 8 levelsincluding node 1. Each W is a binary tree with 5 levels. The tree forset S1 has 1+5+10+20+40+80+160+320=636 nodes. This requires 10 bits torepresent. Each node of the tree for set S1 encodes both the periodicityand the offset. There are 5 nodes at level 2 (2,3,4,5,6). Each of thesenodes has a periodicity T_(SFC) of 5 ms. The offset Δ_(SFC) increasesfrom left to right via a one-to-one mapping from (2,3,4,5,6) to(0,1,2,3,4). This example is a simple subtraction of 2. Alternatively,it can be a mod 5 operation. At level 3, there are 10 nodes (7 to 16)each having a periodicity of 10 ms. Offsets Δ_(SFC) can be derivedeither via subtraction or a mod 10 operation as previously described.

Table 12 lists the relationship between SRS periodicity T_(SFC) and thenode index for set S1. The SRS periodicity T_(SFC) can be extracted fromthe node index via a look-up table and a few comparisons. The SRS offsetΔ_(SFC) can be extracted by performing (Node_Index)mod T_(SFC). Thus SRSperiodicity T_(SFC) and the SRS offset Δ_(SFC) are easily found fromnode index.

TABLE 12 T_(SFC) 5 ms 10 ms 20 ms 40 ms 80 ms 160 ms 320 ms Node 2-77-16 17-36 37-76 77-156 157-316 317-636 Index Range

FIG. 6 illustrates resource sharing tree 600 for set S2. Tree 600 forset S2 has 8 levels and each W is a binary tree with 5 levels. Tree 600for set S1 has 1+2+10+20+40+80+160+320=633 nodes. This requires 10 bitsto represent. Each node of the tree encodes both periodicity T_(SFC) andoffset Δ_(SFC). There are 2 nodes at level 2 (2,3).

Each of these nodes has a periodicity T_(SFC) of 2 ms. Offset Δ_(SFC)increases from left to right in a one-to-one mapping from (2,3) to(0,1). This could be implemented by a simple subtraction of 2.Alternatively, it can be a mod 2 operation. At level 3, there are 10nodes (4 to 13) each having a periodicity T_(SFC) of 10 ms. OffsetsΔ_(SFC) can be derived either via subtraction or a mod 10 operation aspreviously described.

Table 13 lists the relationship between SRS periodicity T_(SFC) and thenode index for set S2 for two alternative codings. The SRS periodicityT_(SFC) can be extracted from the node index via a look-up table and afew comparisons. The SRS offset Δ_(SFC) can be extracted by performing(Node_Index)mod T_(SFC). Thus SRS periodicity T_(SFC) and the SRS offsetΔ_(SFC) are easily found from node index.

TABLE 13 T_(SFC) 2 ms 10 ms 20 ms 40 ms 80 ms 160 ms 320 ms Node 2-34-13 14-33 34-73 74-153 154-313 314-633 Index 7-16 17-36 37-76 77-156157-316 317-636 Range

The designation of which tree is used (set S1 or set S2) can beimplicitly tied to some other system parameter. For example, set S1 maybe used for TDD and set S2 used for FDD. This choice may be tied to somealternate system parameters, broadcast via SIB or tied to some specificvalues of SRS sub-frame configuration. Thus the number of required RRCsignaling bits can be reduced from 13 bits to 11 bits. This is about a15% overhead reduction. This overhead reduction carries no penalty andis achieved by employing efficient source encoding of the periodicityand sub-frame offset. This set of embodiments reduces SIB and RRCsignaling overhead for parameters related to SRS timing using efficientdata structures such as trees. This overhead reduction is especiallyimportant for SIB signaling due to coverage issues.

1. A method of wireless communication including a plurality of fixedbasestations and a plurality of mobile user equipment comprising thesteps of: each basestation transmitting to any user equipment within acorresponding cell a sounding reference signal sub-frame configurationindicating sub-frames when sounding is permitted; each user equipmentwithin said corresponding cell recognizing said sounding referencesignal sub-frame configuration; and each user equipment sounding only atsub-frames when sounding is permitted according to said recognizedsounding reference signal sub-frame configuration.
 2. The method ofclaim 1, wherein: said step of each basestation transmitting a soundingreference signal sub-frame configuration wherein differing basestationsmay transmit differing sounding reference signal sub-frameconfigurations.
 3. The method of claim 1, wherein: said step of eachbasestation transmitting a sounding reference signal sub-frameconfiguration includes transmitting a periodicity T_(SFC), andtransmitting an offset Δ_(SFC); said step of each user equipmentsounding only at sub-frames when sounding is permitted includesmaintaining a sub-frame count C_(SFC), and sounding only ifΔ_(SFC)=(C_(SFC))mod T_(SFC).
 4. The method of claim 3, wherein: saidsteps of transmitting said periodicity T_(SFC) and transmitting saidoffset Δ_(SFC) includes separately coding said periodicity T_(SFC) andsaid offset Δ_(SFC).
 5. The method of claim 3, wherein: said steps oftransmitting said periodicity T_(SFC) and transmitting said offsetΔ_(SFC) includes jointly coding said periodicity T_(SFC) and said offsetΔ_(SFC).
 6. The method of claim 5, wherein: said step of jointly codingsaid periodicity T_(SFC) and said offset Δ_(SFC) codes in 4 bitssuitable for use in frequency division duplex systems as follows:Decimal Binary T_(SFC) Δ_(SFC) 0 0000 1 0 1 0001 2 0 2 0010 2 1 3 0011 50 4 0100 5 1 5 0101 5 2 6 0110 10 0 7 0111 10 1 8 1000 10 2 9 1001 20 010 1010 20 1 11 1011 20 2 12 1100 40 0 13 1101 40 1 14 1110 40 2 15 1111Inf. NA

where: coding of decimal 15 indicates no SRS thus T_(SFC) is infinite,Δ_(SFC) is meaningless and not applicable (NA).
 7. The method of claim5, wherein: said step of jointly coding said periodicity T_(SFC) andsaid offset Δ_(SFC) codes in 4 bits example suitable for use infrequency division duplex systems as follows: Decimal Binary T_(SFC)Δ_(SFC) 0 0000 1 0 1 0001 2 0 2 0010 2 1 3 0011 5 2 4 0100 5 3 5 0101 54 6 0110 10 5 7 0111 10 6 8 1000 10 7 9 1001 20 8 10 1010 20 9 11 101120 10 12 1100 40 11 13 1101 40 12 14 1110 40 13 15 1111 Inf. NA

where: a coding of decimal 15 indicates no SRS thus T_(SFC) is infinite,Δ_(SFC) is meaningless and not applicable (NA).
 8. The method of claim5, wherein: said step of jointly coding said periodicity T_(SFC) andsaid offset Δ_(SFC) codes 5 bits suitable for use in a frequencydivision duplex system as follows: Decimal Binary T_(SFC) Δ_(SFC) 000000 1 0 1 00001 2 0 2 00010 2 1 3 00011 5 0 4 00100 5 1 5 00101 5 2 600110 5 3 7 00111 5 4 8 01000 10 0 9 01001 10 1 10 01010 10 2 11 0101110 3 12 01100 10 4 13 01101 10 5 14 01110 10 6 15 01111 20 0 16 10000 201 17 10001 20 2 18 10010 20 3 19 10011 20 4 20 10100 20 5 21 10101 20 622 10110 40 0 23 10111 40 1 24 11000 40 2 25 11001 40 3 26 11010 40 4 2711011 40 5 28 11100 40 6 29 11101 Optional 30 11110 Optional 31 11111Inf. NA

where: codings decimal 29 and 30 are not defined; and a coding ofdecimal 31 indicates no SRS thus T_(SFC) is infinite, Δ_(SFC) ismeaningless and not applicable (NA).
 9. The method of claim 5, wherein:said step of jointly coding said periodicity T_(SFC) and said offsetΔ_(SFC) codes in 5 bits suitable for use in frequency division duplexsystems as follows: Decimal Binary T_(SFC) Δ_(SFC) 0 00000 1 0 1 00001 20 2 00010 2 1 3 00011 5 0 4 00100 5 1 5 00101 5 2 6 00110 5 3 7 00111 54 8 01000 10 0 9 01001 10 1 10 01010 10 2 11 01011 10 3 12 01100 10 4 1301101 10 5 14 01110 10 6 15 01111 10 7 16 10000 20 0 17 10001 20 1 1810010 20 2 19 10011 20 3 20 10100 20 4 21 10101 20 5 22 10110 20 6 2310111 20 7 24 11000 40 0 25 11001 40 1 26 11010 40 2 27 11011 40 3 2811100 40 4 29 11101 40 5 30 11110 40 6 31 11111 Inf. NA

where: a coding of decimal 31 indicates no SRS thus T_(SFC) is infinite,Δ_(SFC) is meaningless and not applicable (NA).
 10. The method of claim5, wherein: said step of jointly coding said periodicity T_(SFC) andsaid offset Δ_(SFC) codes in 5 bits suitable for use in a frequencydivision duplex system as follows: Decimal Binary T_(SFC) Δ_(SFC) 000000 1 0 1 00001 2 0 2 00010 2 1 3 00011 5 0 4 00100 5 1 5 00101 5 2 600110 5 3 7 00111 5 4 8 01000 10 3 9 01001 10 4 10 01010 10 5 11 0101110 6 12 01100 10 7 13 01101 10 8 14 01110 10 9 15 01111 20 10 16 1000020 11 17 10001 20 12 18 10010 20 13 19 10011 20 14 20 10100 20 15 2110101 20 16 22 10110 40 17 23 10111 40 18 24 11000 40 19 25 11001 40 2026 11010 40 21 27 11011 40 22 28 11100 40 23 29 11101 Optional 30 11110Optional 31 11111 Inf. NA

where: codings decimal 29 and 30 are not defined; and a coding ofdecimal 31 indicates no SRS thus T_(SFC) is infinite, Δ_(SFC) ismeaningless and not applicable (NA).
 11. The method of claim 5, wherein:said step of jointly coding said periodicity T_(SFC) and said offsetΔ_(SFC) codes in 4 bits suitable for use in time division duplex systemsas follows: Decimal Binary T_(SFC) Δ_(SFC) 0 0000 1 0 1 0001 5 1 (a) 20010 5 1 (b) 3 0011 5 2 4 0100 10 0 5 0101 10 1 (a) 6 0110 10 1 (b) 70111 10 2 8 1000 20 0 9 1001 20 1 (a) 10 1010 20 1 (b) 11 1011 20 2 121100 40 0 13 1101 40 1 (a) 14 1110 40 1 (b) 15 1111 Inf. NA

where: codings decimal 1, 2, 5, 6, 9, 10, 13 and 14 are encoded withrespect to UpPTS orthogonal frequency division multiplexing OFDM symbolswith 1(a) meaning a first OFDM symbol determines Δ_(SFC) and with 1(b)meaning a second OFDM symbol determines Δ_(SFC); and a coding of decimal15 indicates no SRS thus T_(SFC) is infinite, Δ_(SFC) is meaningless andnot applicable (NA).
 12. The method of claim 5, wherein: said step ofjointly coding said periodicity T_(SFC) and said offset Δ_(SFC) codes in5 bits suitable for use in time division multiplex systems as follows:Decimal Binary T_(SFC) Δ_(SFC) 0 00000 1 0 1 00001 5 1 (a) 2 00010 5 1(b) 3 00011 5 1 (a) + 1 (b) 4 00100 5 2 5 00101 5 3 6 00110 5 4 7 0011110 1 (a) 8 01000 10 1 (b) 9 01001 10 1 (a) + 1 (b) 10 01010 10 2 1101011 10 3 12 01100 10 4 13 01101 10 7 14 01110 10 8 15 01111 20 1 (a)16 10000 20 1 (b) 17 10001 20 1 (a) + 1 (b) 18 10010 20 2 19 10011 20 320 10100 20 4 21 10101 20 7 22 10110 20 8 23 10111 40 1 (a) 24 11000 401 (b) 25 11001 40 1 (a) + 1 (b) 26 11010 40 2 27 11011 40 3 28 11100 404 29 11101 40 7 30 11110 40 8 31 11111 Inf. NA

where: codings decimal 1, 2, 3, 7, 8, 9, 15, 16, 17, 23, 24 and 25 areencoded with respect to UpPTS orthogonal frequency division multiplexingOFDM symbols with 1(a) meaning a first OFDM symbol determines Δ_(SFC),with 1(b) meaning a second OFDM symbol determines Δ_(SFC) and with1(a)+1(b) meaning that both OFDM symbols determines Δ_(SFC); and acoding of decimal 31 indicates no SRS thus T_(SFC) is infinite, Δ_(SFC)is meaningless and not applicable (NA).
 13. The method of claim 5,wherein: said step of jointly coding said periodicity T_(SFC) and saidoffset Δ_(SFC) codes in 5 bits suitable for use in time divisionmultiplex systems as follows: Decimal Binary T_(SFC) Δ_(SFC) 0 00000 1 01 00001 5 1 (a) 2 00010 5 1 (b) 3 00011 5 1 (a) + 1 (b) 4 00100 5 2 500101 5 3 6 00110 5 4 7 00111 10 1 (a) 8 01000 10 1 (b) 9 01001 10 1(a) + 1 (b) 10 01010 10 2 11 01011 10 3 12 01100 10 6 (a) 13 01101 10 6(b) 14 01110 10 6 (a) + 6 (b) 15 01111 20 1 (a) 16 10000 20 1 (b) 1710001 20 1 (a) + 1 (b) 18 10010 20 2 19 10011 20 3 20 10100 20 6 (a) 2110101 20 6 (b) 22 10110 20 6 (a) + 6 (b) 23 10111 40 1 (a) 24 11000 40 1(b) 25 11001 40 1 (a) + 1 (b) 26 11010 40 2 27 11011 40 3 28 11100 40 6(a) 29 11101 40 6 (b) 30 11110 40 6 (a) + 6 (b) 31 11111 Inf. NA

where: codings decimal 1, 2, 3, 7, 8, 9, 12 to 17, 20 to 25, 28, 29 and30 are encoded with respect to UpPTS orthogonal frequency divisionmultiplexing OFDM symbols with 1(a) meaning a first OFDM symboldetermines Δ_(SFC), with 1(b) meaning a second OFDM symbol determinesΔ_(SFC) and with 1(a)+1(b) meaning that both OFDM symbols determinesΔ_(SFC); and a coding of decimal 31 indicates no SRS thus T_(SFC) isinfinite, Δ_(SFC) is meaningless and not applicable (NA).
 14. The methodof claim 5, wherein: said step of jointly coding said periodicityT_(SFC) and said offset Δ_(SFC) codes in 4 its suitable for use infrequency division multiplex systems as follows: Decimal Binary T_(SFC)Δ_(SFC) 0 0000 1 0 1 0001 2 0 2 0010 2 1 3 0011 5 0 4 0100 5 1 5 0101 52 6 0110 5 3 7 0111 5 0, 1 8 1000 5 2, 3 9 1001 10 0 10 1010 10 1 111011 10 2 12 1100 10 3 13 1101 10 0, 1, 2, 3, 4, 6, 8 14 1110 10 0, 1,2, 3, 4, 5, 6, 8 15 1111 reserved reserved

where: sounding reference signal sub-frames satisfy └n_(s)/2┘modT_(SFC)εΔ_(SFC).
 15. The method of claim 5, wherein: said step ofjointly coding said periodicity T_(SFC) and said offset Δ_(SFC) codes in4 its suitable for use in time division multiplex systems as follows:Decimal Binary T_(SFC) Δ_(SFC) 0 0000 5 1 1 0001 5 1, 2 2 0010 5 1, 3 30011 5 1, 4 4 0100 5 1, 2, 3 5 0101 5 1, 2, 4 6 0110 5 1, 3, 4 7 0111 51, 2, 3, 4 8 1000 10 1, 2, 6 9 1001 10 1, 3, 6 10 1010 10 1, 6, 7 111011 10 1, 2, 6, 8 12 1100 10 1, 3, 6, 9 13 1101 10 1, 4, 6, 7 14 1110reserved reserved 15 1111 reserved reserved

where: sounding reference signal sub-frames are the sub-framessatisfying └n_(s)/2┘mod T_(SFC)εΔ_(SFC); and sounding reference signalsare transmitted only in configured UL sub-frames or UpPTS.
 16. Themethod of claim 5, wherein: said step of jointly coding said periodicityT_(SFC) and said offset Δ_(SFC) includes forming a tree structure with anumber of levels corresponding to a number of permitted periodicitiesT_(SFC) and a number of nodes within each level corresponding to anumber of permitted corresponding offsets Δ_(SFC), numbering nodes ofsaid tree structure starting with 1 at a base node and numbering a levelin left to right order before numbering a next level, and transmitting acorresponding node number.
 17. The method according to claim 16,wherein: said step of each user equipment within recognizing saidsounding reference signal sub-frame configuration includes recognizing aperiodicity T_(SFC) from said tree level of said node number, andrecognizing an offset Δ_(SFC) dependent on said node number.
 18. Themethod according to claim 17, wherein: said step of recognizing anoffset Δ_(SFC) dependent on said node number includes subtracting aconstant from said node number and mapping a difference to a particularoffset Δ_(SFC).
 19. The method according to claim 17, wherein: said stepof recognizing an offset Δ_(SFC) dependent on said node number sets saidoffset Δ_(SFC) to (node number)modulo T_(SFC).
 20. The method of claim1, wherein: said step of each basestation transmitting a soundingreference signal sub-frame configuration includes transmitting aperiodicity T_(SFC), transmitting an offset Δ_(SFC), and transmitting aparameter δ_(SFC); said step of each user equipment sounding only atsub-frames when sounding is permitted includes maintaining a sub-framecount C_(SFC), and sounding ifΔ_(SFC)=(C _(SFC))mod T _(SFC),1+Δ_(SFC)=(C _(SFC))mod T _(SFC),2+Δ_(SFC)=(C _(SFC))mod T _(SFC), orδ_(SFC)+Δ_(SFC)=(C _(SFC))mod T _(SFC).
 21. The method of claim 20,wherein: said parameter δ_(SFC) is a predetermined constant.
 22. Themethod of claim 20, wherein: said parameter δ_(SFC) is inferred from acell ID.
 23. The method of claim 20, wherein: said steps of transmittingsaid periodicity T_(SFC), transmitting said offset Δ_(SFC) andtransmitting a parameter δ_(SFC) includes separately coding saidperiodicity T_(SFC), said offset Δ_(SFC) and said parameter δ_(SFC). 24.The method of claim 20, wherein: said steps of transmitting saidperiodicity T_(SFC), transmitting said offset Δ_(SFC) and transmitting aparameter δ_(SFC) includes jointly coding said periodicity T_(SFC), saidoffset Δ_(SFC) and said parameter δ_(SFC).